This invention relates to corrugated, flexible tubing, especially rubber tubing, including both the helically corrugated type of rubber tubing made using the "cording" method and apparatus disclosed in U.S. Pat. Nos. 2,832,096; 2,879,953; 2,888,712; 2,909,198; 3,155,757; and 3,635,255; and in pending U.S. application Ser. No. 87,512 now abandoned, and also the type of helically or annularly corrugated tubing made using the axially extensible forming member method and apparatus of U.S. Pat. Nos. 3,168,604; 3,304,581; 3,669,586; 3,705,780; 3,809,522; 3,975,129; 4,053,275; 4,133,828; and pending U.S. patent application Ser. No. 87,512. More particularly, the invention relates to a novel variation of the type of corrugated tubular product that may be made using the basic concepts of the methods and apparatus referred to above, and especially to a novel corrugated, tubular rubber product that has unique properties particularly suitable in special applications where prior art tubing has been found to have deficiencies.
Flexible, helically or annularly corrugated rubber tubing of the type described is formed of an extruded sleeve of vulcanizable material which, when cured, provides a homogeneous, flexible, resilient wall structure that often requires a discrete set of properties. These properties are selected to provide the desired characteristics for the particular application. Typical properties are flexibility, hardness, resistance to oxidation and corrosion, tensile strength, arcing resistance, etc.
In some applications, the desired combinations of properties cannot be obtained with a single available vulcanizable composition and the requirements cannot be satisfied by tubing available from the above-recited prior art. For example, in a typical application--namely, vacuum cleaner hose--it is desirable that the interior portion of the hose have a high static conductivity and that the exterior portion be non-marking. These properties are inconsistent, since compositions with a high static conductivity tend not to resist arcing, and compositions that are non-marking have a low static conductivity.
In another typical special application--namely, marine fill hose--it is desirable that the interior portion of the hose gave good oil resistance and that the exterior portion have a high ozone resistance. Here again, these properties are inconsistent, since available compositions with good oil resistance have generally poor ozone resistance, whereas, compositions with good ozone resistance have generally poor oil resistance.
As indicated above, in the past corrugated, flexible tubing has been made using both the "cording" method and the "axially extensible form" method, both methods being described in detail in the aforementioned patents and pending application. Helically corrugated tubing made according to the "cording" method is made by first drawing an extruded sleeve of uncured rubber axially over an elongated, rotatable mandrel with a cord strip wrapped around it to form a single, continuous, external thread. The uncured rubber sleeve is forced into the helical groove or root of the thread by a length of cord wrapped around the sleeve to impart a desired corrugated shape. The rubber sleeve is cured in this condition and the cord removed. After curing, the resulting hose length may be removed from the mandrel and the core strip in a number of ways, such as by being blown off by air pressure from within the mandrel as described in U.S. Pat. 2,888,712.
The resulting helically corrugated hose length is both flexible and strong, yet still maintains its tubular form in a semirigid condition. This type of hose has particular application for use in domestic and industrial vacuum cleaners, as engine exhaust tubing, or tubing for ventilation systems, as well as in other appropriate applications.
Flexible corrugated tubing of the type of which the present invention is directed may also be produced using the "axially extensible form" method, as indicated above. In accordance with this method, external forming devices having axially spaced annular discs or helical convolutions are employed with forming mandrels to produce embryonic corrugations in uncured rubber sleeves. Each time a tube is formed, the forming member is placed over the forming mandrel on which the uncured rubber sleeve has been positioned and the sleeve is radially expanded with air pressure from within so that it bulges into the spaces between the discs or helical convolutions, thus forming creases between the bulges. The external forming member and sleeve are then collapsed axially so that the sleeve is axially compressed concertina fashion. The creases, together with adjacent bulges, provide embryonic corrugations. Then the forming member is axially extended together with the sleeve, after which the sleeve is removed from the forming mandrel and placed on a cylindrical curing mandrel, where it is axially foreshortened, concertina fashion, into corrugated form with the desired spacing between adjacent annular or helical corrugations.
According to a new variation of the above-described "cording" method, as described in pending U.S. patent application Ser. No. 87,512, two helically corrugated tube lengths of different diameter may be formed simultaneously by placing one uncured rubber sleeve on top of the other before the forming operation. According to that method, a parting component or lubricant must be generously applied to the inner sleeve before the outer sleeve is telescoped over it in order to facilitate removal of the two sleeves from one another.
In any event, none of the above-described methods up to now produces a product that satisfies the unique problems described above, wherein certain desired properties for special applications cannot be obtained since often the properties are inconsistent with one another.
The method and product of the present invention, however, resolve the difficulties indicated above and afford other features and advantages heretofore not obtainable.